Hello,
Am Freitag, 3. April 2009 12:12 schrieb Eduardo Valentin:
On Thu, Apr 02, 2009 at 06:36:37PM +0200, ext Hans Verkuil wrote:
On Thursday 02 April 2009 14:02:11 Eduardo Valentin wrote:
Hi Hans,
On Thu, Apr 02, 2009 at 09:47:11AM +0200, ext Hans Verkuil wrote:
On Wednesday 01 April 2009 11:43:28 Eduardo Valentin wrote:
Hello Mauro and v4l guys,
This series contains a v4l2 radio driver which
adds support for Silabs si4713 devices. That is
a FM transmitter device.
As you should know, v4l2 does not contain representation
of FM Transmitters (at least that I know). So this driver
was written highly based on FM receivers API, which can
cover most of basic functionality. However, as expected,
there are some properties which were not covered.
For those properties, sysfs nodes were added in order
to get user interactions.
Comments are wellcome.
Can you explain in reasonable detail the extra properties needed for
a device like this? You will need to document that anyway :-) Rather
than implementing a private API it would be much more interesting to
turn this into a public V4L2 API that everyone can use.
Yes, here is a little description of them:
Pilot is an audible tone sent by the device.
pilot_frequency - Configures the frequency of the stereo pilot tone.
pilot_deviation - Configures pilot tone frequency deviation level.
pilot_enabled - Enables or disables the pilot tone feature.
The si4713 device is capable of applying audio compression to the
transmitted signal.
acomp_enabled - Enables or disables the audio dynamic range control
feature. acomp_gain - Sets the gain for audio dynamic range control.
acomp_threshold - Sets the threshold level for audio dynamic range
control. acomp_attack_time - Sets the attack time for audio dynamic
range control. acomp_release_time - Sets the release time for audio
dynamic range control.
Limiter setups audio deviation limiter feature. Once a over deviation
occurs, it is possible to adjust the front-end gain of the audio input
and always prevent over deviation.
limiter_enabled - Enables or disables the limiter feature.
limiter_deviation - Configures audio frequency deviation level.
limiter_release_time - Sets the limiter release time.
power_level - Sets the output power level for signal transmission.
Hmm, there are two ways to implement these: either make a bunch of
VIDIOC's for each of these categories, or use extended controls to set
all these values. I'm hardly an expert on FM transmitters, but it all
seems reasonable to me (i.e., not too specific for this chip).
I am leaning towards extended controls, since that's so easy to extend if
needed in the future. And I still intend to add sysfs support to controls
in the future. On the other hand, it's a bit harder to use compared to
normal VIDIOCs.
Could you please explain more about extended controls vs. VIDIOC's?
Pointing drivers which uses one of those also would be worth. But yes,
looks like moving this properties to some sort of v4l2 control looks better
implementation.
RDS related
rds_enabled - Enables or disables the RDS feature.
rds_ps_name - Sets the RDS ps name field for transmission.
rds_radio_text - Sets the RDS radio text for transmission.
rds_pi - Sets the RDS PI field for transmission.
rds_pty - Sets the RDS PTY field for transmission.
So you set the fields and the RDS encoder will just start using them?
Once you have rds_enabled set, yes, it will transmit them.
This too can be done with controls (needs some work, though, to support
string controls).
Yes, true.
Region related
Setting region will affect other region properties.
region_bottom_frequency
region_channel_spacing
region_preemphasis
region_top_frequency
I do not know enough about FM transmissions to judge this. Are these
region properties something that is regulated by some standards
commision? Do they also apply when you modulate this over a TV/radio
cable system? Do you have some documentation or links that I can look at
to learn more about this?
stereo_enabled - Enables or disables stereo mode.
How does one pass the audio and rds data to the driver? Note that for
2.6.31 we will finalize the V4L2 RDS decoder API (I recently posted
an RFC for that, but I haven't had the time to implement the few
changes needed). It would be nice if rds modulator support would be
modeled after this demodulator API if possible.
I see. This is good. I think the best way is to have a rds modulator
interface. This driver have implemented it as sys properties, as
described above.
I don't think there is that much overlap, though. The similarities are
probably limited to some flags.
Does region information really belong in the driver? Perhaps
